Determination of moisture in tobacco



De. v26, 1967 v 1. o. PULLMAN 3,360,721

DETERMINATION OF' MOISTURE IN TOBACCO Filed Oct. 30, 1963 3 Sheets-Sheet 1 I NVENTOR. UAMES O, )SULL/IAN A Une/vens Dec. 26, 1967 J, o, PULLMAN 3,360,721

DETERMINATION OF MOISTURE IN TOBACCO 5 sheets-sheet 2 Filed Oct. 30, 1963 NVENTOR. JAMES O. /O/JMMAN ANTW/Veys Dec. 26, 1967 J. O. PULLMAN DETERMINATION OE MOISTURE IN TOBACCO 5 Sheets-Sheet l Filed Oct. 30. 1963 INVNTOR. c//Wc O. /OULLMA/v United States Patent O 3,360,721 DETERMINATION OF MOISTURE IN TOBACCO .lames O. Pullman, Chapel Hill Township, Orange County, N.C., assignor to Liggett & Myers Tobacco Co., New York, N.Y., a corporation of New Jersey Filed Oct. 30, 1963, Ser. No. 320,015 7 Claims. (Cl. S24-58.5)

This invention relates to a method for determining the moisture content in tobacco in particulate form. The invention also relates to apparatus suitable for use in determining the attenuation of microwave energy by tobacco in particulate form.

In the tobacco industry, and more particularly the production of cigarettes, the moisture content of the tobacco is an important variable which should be controlled within narrow tolerances during the various stages of manufacture. The problem of controlling the moisture in tobacco is made more dicult because tobacco is hygroscopic. Thus, the tobacco is able to pick up moisture from the air very readily and thus disturb the balance achieved by previous careful attention to the water content.

Another facet of the moisture problem in cigarette tobacco is that uniformity is perhaps the most important factor in manufacturing cigarettes. A user of a certain brand of cigarettes does not expect any variation in smoking qualities from cigarette to cigarette. The level of moisture in tobacco can affect the smoking qualities, and therefore should be carefully controlled.

A method of measuring moisture for the tobacco industry must provide reproduceable accurate results. If the precision of the method is poor, control of moisture content within narrow tolerances will not be possible.

In making measurements on any material in particulate form, the reproducibility depends on two factors-first, the reproducibility of the actual measurements; and second, the reproducibility of the sample. Thus, it is necessary that the sample to be tested be selected in a certain manner, and handled in a certain manner during the measurement.

It has been found that microwave energy measurement techniques are eminently suited for determining the moisture content of tobacco in particulate form, (for example shredded tobacco or strip tobacco) provided certain procedures and apparatus are employed.

Accordingly, it is an object of this invention to provide a reproduceable method for determining the moisture content in tobacco in particulate form which is based on measurement of the attenuation of energy in the microwave frequency range caused by passage of the energy through a sample of tobacco.

Another object of this invention is to provide an improved apparatus suitable for measuring the attenuation of microwave energy caused by passage through a sample of tobacco in particulate form, the improvement in said apparatus relating to electronic reproducibility due t0 elimination of variables such as reflectance.

A further object of this invention is to provide an improved sample holder for use in measuring the attenuation of microwave energy.

An additional object of this invention is to provide a method of determining the moisture content of tobacco in particulate form `by concurrently measuring the attenuation of microwave energy caused by passage through a sample of the tobacco and the temperature of tobacco sample.

Another object of this invention is to provide a method of determining the moisture content of tobacco in particulate form which involves the use of a sample of .tobacco of a uniform weight, vibrating the sample to ice eliminate non-uniformities in packing, and compressing the sample prior to measuring the attenuation of micro- Wave energy caused by passage through the sample.

Briefly stated, one embodiment of this invention provides an improvement in an apparatus for measuring attenuation of energy in the microwave frequency range of the electromagnetic spectrum caused by passage of said energy -through a sample, the apparatus comprising a source of microwave energy tuned to a specific frequency, a transmit-ting horn connected to said source for beaming the microwave energy at said sample, a receiving horn aligned with said transmitting horn and positioned to receive the microwave energy transmitted by the sample, and means connected to said receiving horn for determining the attenuation caused by said sample, `the said improvement comprising a sample holder in the shape of a hollow cylinder, they wall of said sample holder being constructed of Va material which is electrically conductive, one end of said sample holder being sealed with a disc which is perpendicular to the cylindrical axis of said holder and which has a thickness of 1/2 wave length of the said specific frequency of the microwave energyr source, said disc being transparent to microwave energy, the other end of said holder being adapted to receive and position an internally fitting cap, said cap comprising a terminal portion in the shape of a right rectangular cylinder adapted to be inserted into the other end of said holder, the extremity of said terminal portion being sealed with a disc as aforementioned, said cap being provide-d with positioning means adapted to cooperate with the said other end of said holder so that upon insertion of the terminal portion of the cap into the holder the disc connected to the cap will be at a predetermined location within the holder, the distance between said sealed end of said holder and the disc connected to the cap being approximately equal to of the length of the holder, stationary positioning means located between said receiving horn and said transmitting horn, guide means connected to said holderand adapted to engage said stationary positioning means to reproduceably locate said sample holder between said receiving and transmitting horns so that energy transmitted by said transmitting horn may pass therethrough and impinge upon said receiving horn, said holder being located so that there is no physical contact with either of said horns, elongated temperature probe means adapted to measure the temperature of the sample within said holder, temperature indicator means responsive to said probe means, said probe means being positioned between said horns and oriented with its length perpendicular to the cylindrical axis of said holder, said holder being adapted to admit said probe when said holder is positioned by said guide means and said positioning means whereby a temperature measurement is made simultaneous with the attenuation measurement.

The invention will be more readily understood when described -in conjunction with the drawings in which:

FIG. 1 is a schematic view showing the relationship of the electronic components suitable for use in one embodiment of the present invention,

FIG. 2 is a perspective view of the sample holder of the present invention and the positioning means and other elements associated therewith in accordance with one ernbodiment of this invention,

FIG. 3 is a sectional view of FIG. 2 along the line 3--3 therein,

FIG. 4 is a sectional View of FIG. 3 along the line 4 4 therein, and

FIG. 5 is an exploded perspective view of one embodiment of the sample holder of this invention.

With respect now to the drawings, and more particularly FIG. 1, there is depicted the various electronic com- .'35 ponents conventionally employed for measuring microwave energy attenuation.

Shown in FIG. 1 is a klystron microwave oscillator 10 which produces energy in the microwave region. Modulated power supply 11 furnishes the required operating voltages for oscillator 10, and also provides a modulating voltage which causes the amplitude of the output of oscillator to vary at a frequency in the audio range. Preferably, the oscillator is of the type whose frequency is adjustable in the range of approximately 8,000 to 12,000 megacycles.

The microwave energy from oscillator 10 is introduced into ferrite isolator 12 which serves as a unidirectional element.

The energy is then introduced into a level-set variable attenuator 13. Attenuator 13 is utilized for precisely controlling the amplitude of the microwave energy.

The energy leaving attenuator 13 is introduced into a microwave antenna or horn 14 which focuses the energy into a beam.

Sample holder 15 is shown in the -drawings as being positioned to receive the energy transmitted by horn 14. The details of holder 15 will be described below.

If sample holder 15 contains a material which absorbs microwave energy, the beam of energy leaving holder 15 will be correspondingly reduced. The energy which leaves holder 15 is collected by another microwave antenna or horn 16.

The energy collected by horn 16 is introduced into precision attenuator 17. The purpose of attenuator 17 will be described shortly.

The energy leaving attenuator 17 is introduced into crystal detector 18 which rectifes the alternating input and provides an output which pulsates at the audio frequency at which oscillator 10 is modulated.

The signal produced by detector 18 is amplified by tuned audio amplier 1'9, and the output of amplier 19 is introduced into meter for visual observation.

The various components shown in FIG. 1 are, of course, connected by conventional wave guide sections.

The operation of the apparatus shown in FIG. 1 is briey as follows. Attenuator 17 is adjusted so that it causes a predetermined amount of attenuation on the energy introduced therein. With the sample holder 15 absent, attenuator 13 is adjusted to provide full scale deflection on meter 20. Preferably, amplifier 19 is provided with a gain adjustment and this is used to correct for the aging of electronic components therein, meter departures and the like.

A sample of the material to be tested is introduced into holder 15, and holder 15 is then inserted lbetween horns 14 and 16. Assuming that the material in holder 15 is capable -of absorbing microwave energy, the indicator of meter 20 will drop from its previous full scale reading, thus indicating that the energy reaching it is lower than the calibration level. At this point, attenuator 17 is adjusted to decrease the amount of attenuation caused thereby, and this adjustment is continued until the indicator of meter 20 is again at its full scale position. At this point, the attenuation caused by absorption of microwave energy by the sample in holder 15 has been exactly offset by the decrease in attenuation caused by attenuator 17. Attenuator 17 is provided with an accurately calibrated dial so that the change in setting can be easily determined. This change in setting of the dial of attenuator -17 then represents the attenuation caused -by absorption of microwave energy -by the sample in holder 15.

For general purposes, the deflection of the needle of meter 20 can be used as a measure of the attenuation caused by the sample in holder 15. However, from a quantitative standpoint, this is undesirable since the reading would be subject to errors and variations from many sources, such as non-linearity in detector 18 and/or amplier 19 and the like. By using attenuator 17 to increase the energy fed to crystal detector 18, all of the components following attenuator 17 are returned to the datum level which prevailed under calibration conditions. For dnetails of the operation of a system such as that shown .1n FIG. 1, see Massachusetts Institute of Technology l'adiation Laboratory Series 8, Principles of Microwave Circuits (Montgomery, Dicke and Purcell), McGraw-Hill Book Company, Inc.

It is well known that water responds strongly to an alternating electrical eld in the microwave range. Such response results in absorption of a portion of the energy due to the characteristic vibration of the water molecules.

In view of the foregoing property of water to absorb microwave energy, there is provided a convenient method of measuring the water content in a given material, provided there is no other element present which also absorbs microwave energy. In addition, in order to use this technique to determine the water content of a material, all other variables which could affect attenuation must be substantially eliminated or else compensation provided therefor.

The present invention provides a method of determining the moisture content of tobacco in particulate form which has proven to be reliable, reproduceable and accurate. The advantages of the present invention stem from certain operational steps employed in the actual determination of the attenuation, and also from the manner in which the tobacco sample is formed. In addition, a novel sample holder has been developed which enhances the accuracy of the method of the invention.

FIG. 2 is a perspective view showing sample holder 15, and its relationship to the other elements of the invention. FIG. 2 shows a supporting structure 21 in which are positioned horns 14 and 16.

Holder 15 is shown in detail in FIG. 5. Hollow cylinder 22 is provided to hold the sample of tobacco. Preferably it is constructed from an electrically conductive material to prevent the escape of any microwave energy through the walls. A disc 23 of material transparent to microwave energy is used as a seal for end 24 of cylinder 22. It is conveniently attached by screws (not shown) which engage the wall of cylinder 22, and screw holes 25 are depicted in disc 23 for this purpose.

The other end of holder 15 is designed to admit cap 26, discussed in detail below. To this end, the inside diameter of the terminal portion 46 of holder 15 has been enlarged thereby forming shoulder 47.

Cap 26 is cylindrical in shape and has two portions of differing diameter, the elongated portion 27 having an outside diameter approximately equal to the diameter of terminal portion 46 of cylinder 22 thereby permitting it to be inserted therein. The wall thickness of portion 27 of cap 26 is made equal to the width of shoulder 47. Thus, when cap 26 is inserted into holder 15, there is no discontinuity in the internal surface of holder 15.

The larger diameter portion 2.8 of cap 26 in conjunction with shoulder 47 serves as a stop which prevents further movement of portion 27 into the interior of cylinder 22. A disc 29 of material transparent to microwave radiation is attached to the end 30 of cap 26 and serves as a seal.

FIG. 4 is a sectional view showing holder 15 with cap 26 in place. In order to securely hold cap 26 in place, locking means are provided. Conveniently, these locking means are raised catch 31 which is attached to the periphery of cylinder 22, and latch 32 which is attached to the periphery of portion 28 of cap 26. Since catch 31 is partially spaced from the surface of cylinder 22, latch 32 slides thereunder in frictional engagement therewith. This relationship is best seen in FIG. 2.

Holder 15 is provided with handles 33 having slots 34 therein to facilitate handling cylinder 22.

Handles 33 also function as guide means. As shown vin thevdrawings,lthere is a V-shaped slot 36 cut in each of the handles 33. Inverted V-shaped blocks 37 are attached to structure 21, as shown in FIG. 2. When the holder 15 is introduced between horns 14 and 16, V-

shaped slots 36 eng'ag'e inverted V-shaped blocks 37,

. thereby reproduceably locating holder 15 with respect to horns 14 and 16.

With respect to FIG. 2, there is depicted a pair of resilient bumpers 38 which are connected toy structure 21. These bumpers serve to maintain holder 15 rmly in place.

Blocks 39 are attached to structure 21 and serve as stops to align holder 15 with the apertures 40 and 41 of horns 1-4 and 16, respectively.

FIG. 1 schematically depicts temperature indicator 42 which is connected to temperature probe 43. These are provided in order to enable a temperature measurement to be made simultaneously with the attenuation measurement.

FIGS. 2 and 3 illustrate the location of temperature probe 43 with respect to the other elements of the apparatus. To minimize interaction with the microwave field, the longitudinal axis of probe 43 should be oriented parallel to the magnetic vector of the microwave energy. Temperature probe 43 is a fast-response probe having a tip 45 which comprises a temperature-sensitive thermistor.

As shown in FIG. 4, holder 15 is provided with an opening 44 which is adapted to receive temperature probe 43. Thus when holder 15 is located by guides 36 and 37, opening 44 is positioned to admit temperature probe 43. FIG. 3 illustrates probe 43 in position within holder 15.

The temperature sensed by probe 43 is displayed on temperature indicator 42, shown schematically in FIG. l.

By measuring the temperature of the sample at the time the attenuation is determined, any non-reproducibility of microwave energy absorption due to variation in temperature can be eliminated. A temperature calibration chart of temperature versus moisture correction factor may be obtained as follows. Samples of tobacco are prepared having various moisture levels. Microwave attenuation measurements in accordance with the procedure outlined herein are then made on the tobacco samples at different temperatures. The amount of moisture in the tobacco samples is determined beforehand by quantitative analysis. Then, a group of data are obtained showing the variations in microwave attenuation for a sample of Agiven moisture content when measured at various temperature-s. In this manner, a family of curves of attenuation versus moisture content at specific temperatures may be constructed.

The preferred method of measuring the moisture in tobacco in particulate form comprises several steps. First, a standard weight of sample is utilized. This standard weight should have a volume which will approximately fill -holder 15. In other words, holder 15 is placed in an upright position with disc 23 on the bottom and with cap 26 removed. The particulate tobacco is then introduced into holder 15, the preweighed sample substantially lling the holder.

An important consideration in the measurement of the attentuation of a sample is that the sample should be as uniform as possible with respect to the absence of voids or overly dense areas. To this end, it is preferable that .holder 15 be mounted on a vibrating surface, 'such as a conventional vibrating table during the filling operation. In this manner the tendency toward a non-homogenous sample structure is avoided.

The sample within holder 15 is then compressed by placing cap 26 in its proper position within holder 15. As can be seen in FIG. 4, when cap 26 is positioned properly Within holder 15, disc 29 extends partially into the interior of holder 15. Thus the sample volume is compressed in proportion to the relative dimensions of holder 15 and elongated portion 27 of cap 26. The compression of the sample is considered to aid in the reproducibility of attenuation measurements made in accordance with the method of the present invention.

The filled sample holder 15 is then introduced between transmitting horn 14 and receiving lhorn 16, as shown in FIG. 2. The V-shaped slots 36 in handle 33 engage inverted V-shaped blocks 37, and thus in conjunction with bumpers 38 and blocks 39 serve to reproduceably position holder 15 between horns 14 and 16.

At this point, the attenuation measurement is made as described above and the temperature measurement is made, and compensation provided, if necessary.

As indicated above, the setting of the dial of attenuator 17 is preferably utilized as a measure of the attenuation caused by the sample. By suitable calibration techniques, the dial of attenuator 17 may be designed so as to read directly in moisture content.

A potential source of error in measuring attenuation with the apparatus described herein is from the non-reproducibility of reected microwave energy. In order to reduce this error as low as possible, disc 23 of holder 15 and disc 29 of cap 26 are designed to have a thickness of one-half of a wavelength (in the dielectric material of which the discs are formed) of the specific frequency being utilized.

In addition to the above, the respective apertures of horns 14 and 16 are chosen to be approximately equal to the inside diameter of sample holder 15. This provides a narrow or parallel beam so that substantially all of the microwave energy emanating from transmitting horn 14 must pass through the sample in sample holder 15.

The shape of the sample holder and the relative dimensions thereof are also factors which are important in obtaining accurate att-enuation measurements. A cylindrical sample holder is preferred to one which is square, for example, because the cylindrical holder can be more readily packed in a uniform manner. The square corners of `a square cross-sectioned holder would tend to cause irregularities and non-uniformities in and about the corners, and therefore some degree of reproducibility would |be lost.

Preferably, sample holder 15 should have a length which is greater than its diameter. If it could be assured that each sample would have an ideally uniform structure, i.e. be completely homogenous, then the relative dimensions of the holder would be 'of no importance. The above choice of relative dimensions of holder 15 is based on the supposition that it is not possible to achieve cornplete uniformity or homogeneity in the sample.

Each molecule of water present in the sample 'has a capacity of absorbing microwave energy. A sample holder designed to assure that all of the microwave energy will impinge on all of the molecules of water in the sample will result in =a true attenuation for the sample. Ideally, this could be accomplished by having a sample h'older of infinite length and infinitesimal cross section.

When packing a holder of practical dimensions, such as that shown in the drawings, it is possible that non-uniformities can occur in two ways or in a combination 'of these two ways. First, the particulate tobacco may be present in stratifying 'layers which are perpendicular to the path of the microwave energy. Each of these layers is assumed to be completely uniform but each layer differs in density from each succeeding layer. In such instance, the observed attenuation of microwave energy would be the true aver- =age attenuation since each segment of the beam of microwave energy passes through the same weight of tobacco and therefore passes through or impinges upon the same number of molecules of water.

The second non-uniform condition would be one in which the packing is uniform in any one path through sample holder 15, parallel to the beam of microwave energy, but each such path has a different packing density from each other. Simply, this could be illustrated by assuming that half of the interior of holder 15, sliced longitudinally, has one density `and the other half has a second, different density. In such instance, the attenuation measured would not be the true average attenuation.

In the practical situation, the packing achieved is probably a combination of both types of non-uniformity. Thus, it is expedient to make the sample holder 15 greater in |length than its diameter in order to achieve as much averaging as possible. It can be seen that with a very short sample holder, non-uniformities of the second type described above would be very diicult to average out.

The embodiments shown in the drawings are intended to be illustrative of one type of apparatus suitable for carrying out the process of the present invention. Variations both in the -process described and in the apparatus disclosed may be made by one skilled in the art without departing from the spirit and scope of this invention.

What is claimed is:

1. In a system for determining the moisture contained in a sample of tobacco in particulate form by measuring the attenuation of micro-wave energy beamed from the aperture of a transmitting horn through the sample of tobacco to the aperture olf a receiving horn, the improvement of a holder for the sample of tobacco, said holder comprising:

(a) a hollow right rectangular cylinder constructed of electricially conductive material, said cylinder having a circular cross-section,

(ib) the inside diameter of said cylinder being substantially equal to the greatest distance across the apertures of said micro-wave horns,

(c) end caps at each end lof said cylinder, said end caps being transparent to micro-wave energy, and

(d) suppport means for supporting said holder spaced between said horns without physical cont-act between said holder and said horns.

2. The holder of claim 1 further characterized by: the axial length of said cylinder being greater than the diameter of said cylinder.

3. The holder of claim 1 `further characterized by: means zfor compressing by a predetermined amount whatever particulate matter may be placed in said cylinder.

4. The holder of claim 1 further characterized by: a temperature sensing probe extending through said cy-linder wall, the axis of said probe being perpendicular to the axis of said cylinder.

5. In a system for determining the moisture contained in a sample of tobacco by measuring the attenuation of micro-wave energy beamed from a transmitting horn through the sample of tobacco to a receiving horn, the

improvement of a holder for the sample of tobacco, said holder comprising:

(a) a hollow right circular cylinder constructed of electrically conductive material, i

(b) end caps at each end of said cylinder, said end caps being transparent to micro-wave energy,

(c) means for compressing by -a predetermined amount the tobacco placed in said cylinder, and

(d) support means for supporting said holder spaced -fbetween said horns wit-hout physical contact between said holder and either of said horns.

6. The holder of claim 5 further characterized by: the axial length of said cylinder being greater than the diameter of said cylinder.

7. The holder of claim 5 further characterized by: a temperature sensing probe extending through said cylinder wall, the axis of said probe being perpendicular to the axis `of said cylinder.

References Cited UNITED STATES PATENTS 2,082,364 6/1937 Store 324-65.1 2,581,950 9/1952 Glegg 324-65 2,611,804 9/1952 Zaleski 324-58.5 2,613,251 10/ 1952 Ebert 324-58 2,659,860 11/1953 Breazeale 324-58.5 2,724,798 11/1955 Hare et al 324-61 2,755,438 7/1956 Cudmore 324-65 2,798,197 7/1957 Thurston 324 58.5 3,115,131 12/1963 Holliday 324-58.5 XR

FOREIGN PATENTS 1,102,199 5/1955 France.

592,450 9/ 1947 Great Britain.

OTHER REFERENCES Army Technical Manual, June 1953, page 69.

RUDOLPH V. ROLINEC, Primary Examiner.

WALTER L. CARLSON, Examiner.

P. F. WILLIE, A. E. RICHMOND,

Assistant Examiners. 

1. IN A SYSTEM FOR DETERMINING THE MOISTURE CONTAINED IN A SAMPLE OF TOBACCO IN PARTICULATE FORM BY MEASURING THE ATTENUATION OF MICRO-WAVE ENERGY BEAMED FROM THE APERTURE OF A TRANSMITTING HORN THROUGH THE SAMPLE OF TOBACCO TO THE APERTURE OF A RECEIVING HORN, THE IMPROVEMENT OF A HOLDER FOR THE SAMPLE OF TOBACCO, SAID HOLDER COMPRISING: (A) A HOLLOW RIGHT RECTANGULAR CYLINDER CONSTRUCTED OF ELECTRICALLY CONDUCTIVE MATERIAL, SAID CYLINDER HAVING A CIRCULAR CROSS-SECTION. (B) THE INSIDE DIAMETER OF SAID CYLINDER BEING SUBSTANTIALLY EQUAL TO THE GREATEST DISTANCE ACROSS THE APERTURES OF SAID MICRO-WAVE HORNS, (C) END CAPS AT EACH END OF SAID CYLINDER, SAID END CAPS BEING TRANSPARENT TO MICRO-WAVE ENERGY, AND (D) SUPPORT MEANS FOR SUPPORTING SAID HOLDER SPACED BETWEEN SAID HORNS WITHOUT PHYSICAL CONTACT BETWEEN SAID HOLDER AND SAID HORNS. 